A. Technical Field
The present invention relates to a production process for a hydroxyalkyl (meth)acrylate, which comprises the step of carrying out a reaction between (meth)acrylic acid and an alkylene oxide in the presence of a catalyst.
B. Background Art
What have hitherto been common as production processes for a hydroxyalkyl (meth)acrylate involving a batch reaction between (meth)acrylic acid and an alkylene oxide are: a process that involves the step of charging a reaction vessel with (meth)acrylic acid and an alkylene oxide (which are raw materials) along with a catalyst in a lump to thus carry out their reaction; and a process that involves the steps of charging a reaction vessel with (meth)acrylic acid (which is a raw material) and a catalyst both in their entirety and thereafter adding an alkylene oxide thereto gradually (continuously or intermittently) at a constant or variable supplying rate to thus carry out their reaction. The reasons therefor are such that: the (meth)acrylic acid has higher catalyst-dissolving ability than the alkylene oxide; and, if the alkylene oxide is initially charged alone into the reaction vessel and then heated, there is involved a danger of explosion, and therefore special facilities for coping with this danger are needed. Even in the former process that involves the step of charging the reaction vessel with the (meth)acrylic acid and the alkylene oxide along with the catalyst in a lump to thus carry out their reaction, it is actually a conventional procedure to charge the (meth)acrylic acid earlier than the alkylene oxide.
However, both in the above processes, there is a problem such that: a dialkylene glycol mono(meth)acrylate (which is an alkylene oxide's diaddition product and may hereinafter be referred to simply as “alkylene oxide's diaddition product”) tends to be by-produced as an impurity, therefore the resultant product is so low in purity as to be bad in quality. In addition, as a matter of fact, the alkylene oxide's diaddition product as by-produced can be removed in the distillation step after the reaction step. However, it is inevitable that, as the alkylene oxide's diaddition product is more and more by-produced in the reaction step, the yield of the hydroxyalkyl (meth)acrylate (which is the objective product) becomes lower. Therefore, as to the reaction stage, it is strongly desired to suppress the side production of the above alkylene oxide's diaddition product as much as possible, with the amount of the produced objective product kept as large as conventional, or larger.